Fc FUSION HIGH AFFINITY IgE RECEPTOR ALPHA-CHAIN

ABSTRACT

Provided is an Fc fusion high affinity IgE receptor α-chain having excellent stability at low pH. An Fc fusion protein comprising:
         (i) a high affinity IgE receptor α-chain; and   (ii) an Fc region of IgG1, wherein   a linker fragment region between the (i) and the (ii) is the amino acid sequence shown in SEQ ID NO: 2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/552,065, which is a National Stage application of PCT/JP2016/054854,filed Feb. 19, 2016, which claims priority from Japanese applicationnos. JP 2015-032231, filed Feb. 20, 2015, and JP 2015-252231, filed Dec.24, 2015.

The instant application contains a Sequence Listing which has beensubmitted in ASCII format via EFS-WEB and is hereby incorporated byreference in its entirety. Said ASCII copy, created on Jul. 10, 2018, isnamed sequence.txt and is 10 KB.

TECHNICAL FIELD

The present invention relates to an Fc fusion high affinity IgE receptorα-chain that is useful as a pharmaceutical product.

More specifically, the present invention relates to an Fc fusion highaffinity IgE receptor α-chain having excellent stability at low pH, anda medicinal use thereof.

BACKGROUND ART

Immunoglobulin E (IgE) is one of an immunoglobulin group, which plays arole in allergic reactions. The IgE, which is secreted from B cells oris expressed on the surface of the B cells, binds to a high affinity IgEreceptor (FcεRI) found on the surface of mast cells, basophils, etc.When an antigenic protein binds to IgE on a mast cell surface receptor,the IgE becomes a form in which it crosslinks the antigen. Thereafter,chemical mediators such as histamine or serotonin, which are stored inintracellular granules, are released. Consequently, an inflammatoryreaction is induced, and type I allergy symptoms such as telangiectasisor vascular hyperpermeability are provoked (Non Patent Literature 1).

Accordingly, since a compound or a protein, which inhibits the bindingof IgE to FcεRI, inhibits the binding of the IgE to the FcεRI found onthe surface of mast cells, basophils, etc., such a compound or a proteinis expected as a therapeutic agent for type I allergic diseases such asbronchial asthma, allergic rhinitis, and allergic conjunctivitis (NonPatent Literature 2).

In recent years, not only a conventional pharmaceutical productcomprising, as an active ingredient, a low-molecular-weight compound,but also a protein pharmaceutical product, which strongly binds to aspecific receptor or the like in a living body and exhibits excellenttherapeutic effects, has been developed. For example, Etanercept hasbeen known as a therapeutic agent for rheumatoid arthritis. SuchEtanercept is a completely humanized soluble TNFα/LTα receptorformulation, which has been focused because of the role of a solublereceptor of a tumor necrosis factor (TNF) to suppress the action of TNFin a living body, and has been then developed.

The protein pharmaceutical product can be expected to have hightherapeutic effects. On the other hand, it may cause a problem specificto the protein pharmaceutical product in the production process thereof.

In general, when an antibody or an Fc fusion protein is produced in theform of a pharmaceutical product, a purification method of using proteinA is applied. In this method, a buffer with a low pH value is used toelute a protein of interest that binds to the protein A. Moreover, inorder to inactivate virus, the protein of interest is desirably treatedat low pH for a certain period of time.

A protein, which is poor in stability at low pH, easily formsaggregates. If the ratio of aggregates is high, a reduction inpurification efficiency or production amount occurs in the production ofprotein pharmaceutical products. In addition, an immune response isprovoked by mixing aggregates into pharmaceutical products, and as aresult, serious side effects, such as anaphylaxis, are likely to occur.

As such, the instability of a protein of interest at low pH may beproblematic in the production of protein pharmaceutical products.

A polypeptide (immunoadheson) comprising an immunoglobulin and anextracellular domain is disclosed in Patent Literature 1. PatentLiterature 1 discloses a high affinity IgE receptor as an example ofsuch immunoadheson. However, this publication does not specificallydescribe a fused protein of a high affinity IgE receptor and animmunoglobulin.

A fused protein (hereinafter referred to as “Fusion protein A”) of ahigh affinity IgE receptor α-chain (FcεRI α-chain; hereinafter referredto as “FCER1A”) and immunoglobulin G1 (IgG1) is disclosed in Non PatentLiterature 3. However, the Fusion protein A disclosed in theaforementioned publication is largely different from the protein of theinvention of the present application, in terms of the mode of bindingFCER1A to IgG1 (Fc). That is to say, the protein of the invention of thepresent application has a characteristic amino acid sequence in a linkerfragment region between the FcεRI and the IgG1.

A fused protein (NPB301) formed by linking a water-soluble fragment ofthe high affinity IgE receptor (FcεRI) to a human Fc region via apeptide linker is disclosed in Patent Literature 2. However, the proteinof the invention of the present application does not comprise thepeptide linker disclosed in Patent Literature 2. Moreover, PatentLiterature 2 neither discloses nor suggests the characteristic aminoacid sequence of the linker fragment region of the present invention.

A fused protein of FCER1A and immunoglobulin G2 (IgG2) is disclosed inPatent Literature 3. However, this fused protein comprising IgG2 isdifferent from the protein of the invention of the present application,in terms of the amino acid sequences of a linker fragment region and anFc region.

A fused protein of non-human primate FCER1A and IgG1 is disclosed inPatent Literature 4. Moreover, a fused protein of FCER1A and IgG1 isdisclosed in Patent Literatures 5 to 7. However, these publicationsneither disclose nor suggest the characteristic amino acid sequence ofthe linker fragment region of the present invention.

The aforementioned Non Patent Literature 3 and Patent Literatures 1 to 7neither disclose nor suggest the protein of the present invention.

CITATION LIST Patent Literature

-   Patent Literature 1: U.S. Pat. No. 5,565,335-   Patent Literature 2: International Publication WO 2012/169735-   Patent Literature 3: Chinese Patent Application Laid-Open No.    101633698-   Patent Literature 4: International Publication WO 2008/028068-   Patent Literature 5: International Publication WO 2011/056606-   Patent Literature 6: International Publication WO 2008/099178-   Patent Literature 7: International Publication WO 2008/099188

Non Patent Literature

-   Non Patent Literature 1: Chisei Ra, “Allergy no Bunshi Saibo Kiko    (Molecular and Cellular Mechanisms of Allergy),” BIO INDUSTRY, 2008,    Vol. 25, No. 9, PP. 23-39-   Non Patent Literature 2: Chisei Ra et al., “International    Immunology,” 1993, Vol. 5, No. 1, PP. 47-54-   Non Patent Literature 3: M. Haak-Frendscho et al., “Journal of    Immunology,” 1993, Vol. 151, No. 1, PP. 351-358

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to provide an Fc fusion highaffinity IgE receptor α-chain having excellent stability at low pH.

Solution to Problem

The present inventors have conducted intensive studies in order toobtain an Fc fusion high affinity IgE receptor α-chain having highstability against low pH or heat. As a result, the inventors have foundthat an Fc fusion high affinity IgE receptor α-chain having highstability can be obtained by using a linker fragment comprising threeCys residues, in a fused protein comprising a high affinity IgE receptorα-chain and the Fc region of IgG1, thereby completing the presentinvention. Specifically, the present invention is as follows.

The present invention relates to the following [1] to [5], etc.

-   [1] An Fc fusion protein comprising:

(i) a high affinity IgE receptor α-chain; and

(ii) an Fc region of IgG1, wherein

a linker fragment region between the (i) and the (ii) is the amino acidsequence shown in SEQ ID NO: 2.

-   [2] The Fc fusion protein according to the above [1], comprising the    amino acid sequence shown in SEQ ID NO: 3, or an amino acid sequence    comprising a deletion of lysine (K) at the C-terminus of the amino    acid sequence shown in SEQ ID NO: 3.-   [3] The Fc fusion protein according to the above [1] or [2], which    is a dimer.-   [4] The Fc fusion protein according to the above [3], wherein    cysteine residues in the linker fragment region form three disulfide    bonds.-   [5] A pharmaceutical composition comprising, as an active    ingredient, the Fc fusion protein according to any one of the above    [1] to [4].

The present description includes the contents as disclosed in JapanesePatent Application No. 2015-032231 and 2015-252231, which are prioritydocuments of the present application.

Advantageous Effects of Invention

The protein of the present invention has excellent stability at low pH.In addition, the protein of the present invention has excellentneutralizing activity against IgE. Accordingly, the protein of thepresent invention is useful as a protein pharmaceutical product forpreventing or treating type I allergic diseases mediated by IgE.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the activity of inhibiting the binding of human IgE. In thefigure, the horizontal axis indicates the concentration of each drug(mol/L); and the longitudinal axis indicates the value of the amount ofIgE bound to Protein 1 immobilized on a plate, which is shown at apercentage (free IgE (percent with respect to a control)), using, as areference, the binding amount obtained when a predetermined amount ofIgE is added. In the figure, the circle indicates the value of Protein1, and the square indicates the value of Omalizumab, respectively.

FIG. 2 shows a transition of a change in the content rate (%) ofaggregates at low pH. In the figure, the horizontal axis indicates thenumber of days (Day), and the longitudinal axis indicates a change inthe content rate (%) of aggregates. In the figure, the circle indicatesthe value of Protein 1, and the square indicates the value of Fusionprotein A, respectively.

FIG. 3 shows a transition of a change in the content rate (%) ofaggregates by a heat treatment. In the figure, the horizontal axisindicates the number of days (Day), and the longitudinal axis indicatesa change in the content rate (%) of aggregates. In the figure, thecircle indicates the value of Protein 1, and the square indicates thevalue of Fusion protein A, respectively.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention will be described in detailbelow.

In the present invention, individual terms have the following meanings,unless otherwise specified.

In the present invention, the “high affinity IgE receptor α-chain(FCER1A)” means a protein comprising an α-chain portion that is anextracellular domain of a high affinity IgE receptor. The high affinityIgE receptor α-chain is, for example, a protein shown in the followingSEQ ID NO: 1.

SEQ ID NO: 1: VPQKPKVSLNPPWNRIFKGENVTLTCNGNNFFEVSSTKWFHNGSLSEETNSSLNIVNAKFEDSGEYKCQHQQVNESEPVYLEVFSDWLLLQASAEVVMEGQPLFLRCHGWRNWDVYKVIYYKDGEALKYWYENHNISITNATVEDSGTYYCTGKVWQLDYESEPLNITVIKAPREKYWL

The above-described high affinity IgE receptor α-chain includes, forexample, a protein having identity of 90% or more, 95% or more, 97% ormore, or 99% or more to the amino acid sequence shown in SEQ ID NO: 1,when the identity is calculated using BLAST (Basic Local AlignmentSearch Tool at the National Center for Biological Information) or thelike (e.g., using default parameters), and having binding ability toIgE. Moreover, the high affinity IgE receptor α-chain also includes aprotein comprising an amino acid sequence having a substitution,deletion and/or addition of one or more, or several amino acids (1 to10, preferably 1 to 5, and more preferably 1 or 2 amino acids) withrespect to the amino acid sequence shown in SEQ ID NO: 1, and havingbinding ability to IgE.

In the present invention, the “Fc region of IgG1” means the Fc fragmentof immunoglobulin G1, namely, the CH2 and CH3 constant domains of nativeimmunoglobulin G1. The Fc region of IgG1 includes all of a naturalmutant, an artificial mutant, and a truncated form.

In the present invention, the “linker fragment region between the highaffinity IgE receptor α-chain and the Fc region of IgG1” means a regionconsisting of 14 amino acid residues ranging from the junction pointbetween the above-described high affinity IgE receptor α-chain and theabove described Fc region of IgG1 towards the direction of the Fcregion.

In the present invention, the “Fc fusion protein” means a recombinantprotein comprising the high affinity IgE receptor α-chain and the Fcfragment of an immunoglobulin.

The protein of the present invention is characterized in that the linkerfragment region between the high affinity IgE receptor α-chain and theFc region of IgG1 is the amino acid sequence shown in the following SEQID NO: 2.

SEQ ID NO: 2: EPKSCDKTHTCPPC

The protein of the present invention is preferably an Fc fusion proteincomprising the amino acid sequence shown in the following SEQ ID NO: 3(hereinafter referred to as “Protein 1”).

SEQ ID NO: 3: VPQKPKVSLNPPWNRIFKGENVTLTCNGNNFFEVSSTKWFHNGSLSEETNSSLNIVNAKFEDSGEYKCQHQQVNESEPVYLEVFSDWLLLQASAEVVMEGQPLFLRCHGWRNWDVYKVIYYKDGEALKYWYENHNISITNATVEDSGTYYCTGKVWQLDYESEPLNITVIKAPREKYWLEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFScSVMHEALHNHY TQKSLSLSPGK

The amino acid sequence shown in SEQ ID NO: 3 has a sequence formed byfusing the amino acid sequence shown in SEQ ID NO: 1 (from Val atposition 1 to Leu at position 179 of the amino acid sequence shown inSEQ ID NO: 3), the amino acid sequence shown in SEQ ID NO: 2 (Glu atposition 180 to Cys at position 193 of the amino acid sequence shown inSEQ ID NO: 3), and the amino acid sequence of the Fc fragment of animmunoglobulin (Pro at position 194 to Lys 411 of the amino acidsequence shown in SEQ ID NO: 3) in this order. This Fc fusion proteinincludes a protein comprising an amino acid sequence having identity of90% or more, 95% or more, 97% or more, or 99% or more to the amino acidsequence shown in SEQ ID NO: 3, which is other than the amino acidsequence portion from Glu at position 180 to Cys at position 193 thatcorresponds to the amino acid sequence shown in SEQ ID NO: 2, when theidentity is calculated using, for example, BLAST (Basic Local AlignmentSearch Tool at the National Center for Biological Information) or thelike (e.g., using default parameters), and having binding ability toIgE. Moreover, this Fc fusion protein includes a protein comprising anamino acid sequence having a substitution, deletion and/or addition ofone or more, or several amino acids (1 to 10, preferably 1 to 5, andmore preferably 1 or 2 amino acids) with respect to the amino acidsequence shown in SEQ ID NO: 3, which is other than the amino acidsequence portion from Glu at position 180 to Cys at position 193 thatcorresponds to the amino acid sequence shown in SEQ ID NO: 2, and havingbinding ability to IgE.

Upon the production of a recombinant antibody, there is a case where thelysine at the C-terminus is deleted by post-translational modification.Accordingly, the protein of the present invention may be an Fc fusionprotein comprising an amino acid sequence having a deletion of thelysine (K) at the C-terminus of the above-described Protein 1. Forexample, such an Fc fusion protein comprising an amino acid sequencehaving a deletion of the lysine (K) at the C-terminus of Protein 1 shownin SEQ ID NO: 3 consists of an amino acid sequence portion from theposition 1 to the position 410 of the amino acid sequence shown in SEQID NO: 3.

The protein of the present invention includes both a monomer and a dimerof an Fc fusion protein formed by linking a high affinity IgE receptorα-chain to the Fc region of IgG1 via a linker fragment consisting of theamino acid sequence shown in SEQ ID NO: 2. Three Cys residues arepresent in the above-described linker fragment region (the Cys residuesat positions 184, 190, and 193 of the amino acid sequence shown in SEQID NO: 3), and a dimer can be formed by disulfide bonds. In general, twoFc fusion protein monomers form a dimer as a result of the formation ofthree disulfide bonds between Cys residues at the same positions asthose of the above-described three Cys residues, and the above-describedthree Cys residues. Because of the above-described three disulfidebonds, a dimer is stabilized, and it has high stability against low pHand heat. The phrase “having high stability against low pH and heat”means, for example, that only a few aggregates are formed underconditions of low pH and under heating. Such high stability against lowpH or heat can be confirmed, for example, by performing a low pHtreatment or a heat treatment on a protein, and then measuring thecontent of aggregates in the protein by gel filtration chromatography.For example, even if the Fc fusion protein of the present invention ispreserved at a low temperature of 2° C. to 8° C., and preferably 4° C.,at pH 1 to 5, and preferably at pH 2 to 4, for 1 day to 1 month,preferably for 1 day to 14 days, and more preferably for 5 to 12 days,or even if the present Fc fusion protein is preserved at a temperatureof 25° C. to 45° C., and preferably 30° C. to 40° C., for 1 day to 1month, preferably 1 day to 14 days, and more preferably 1 day to 7 days,a change in the content rate of aggregates is small. For example, when achange in the content rate of aggregates in the protein of the presentinvention is calculated based on the peak area of gel filtrationchromatography, it is 10% or less, and preferably 8% or less. Further,when compared with an Fc fusion protein having two or less Cys residuesas a linker fragment, a change in the content rate of aggregates in theprotein of the present invention is small.

The protein of the present invention can be produced, for example, bythe following method or a method equivalent thereto, or by the methodsdescribed in publications or methods equivalent thereto.

The protein of the present invention can be produced using a geneticrecombination technique that is well known to a person skilled in thepresent technical field. For example, DNA encoding the protein of thepresent invention is prepared, and an expression vector comprising thisDNA is then constructed. Subsequently, prokaryotic or eukaryotic cellsare transformed or transfected with the above-described vector, and aprotein of interest can be isolated and purified from a culturesupernatant of the obtained cells.

The protein of the present invention can also be produced usingprotein-expressing cells that are well known to a person skilled in thepresent technical field. For example, cDNA encoding the amino acidsequence shown in SEQ ID NO: 3 is incorporated into a mammalianexpression plasmid vector to prepare a protein expression plasmid, andthe prepared plasmid is then introduced into animal cells such asChinese hamster ovary cells (CHO), so as to establish a stableexpression cell line. The obtained cells are cultured, and then, theprotein of the present invention can be obtained from a culturesupernatant.

The protein of the present invention can be isolated and purified, asnecessary, by isolation and purification means that are well known to aperson skilled in the present technical field. Examples of the isolationand purification method include affinity chromatography, ion exchangechromatography, gel filtration chromatography, hydrophobicchromatography, mixed mode chromatography, dialysis, a fractionalprecipitation method, and electrophoresis. The protein of the presentinvention can also be isolated and purified by combining these methodswith one another, as appropriate.

The protein of the present invention may also undergo chemicalmodification that is well known to a person skilled in the presenttechnical field. Examples of the chemical modification includeglycosylation, polyethylene glycolation (PEG), acetylation, andamidation.

Since the protein of the present invention has neutralizing activityagainst IgE, it can be used as a preventive or therapeutic agent forvarious diseases mediated by IgE. For instance, the protein of theinvention of the present application is useful as a preventive ortherapeutic agent for diseases associated with type I allergy, and thelike, such as bronchial asthma, eosinophilic otitis media, eosinophilicsinusitis, allergic conjunctivitis, allergic rhinitis, pollinosis, foodallergy, mite allergic disease, hives, and anaphylactic shock.

The protein of the present invention has excellent affinity for IgE.Hence, the protein of the present invention can also be used as a“protein-drug conjugate” that utilizes such affinity, such as anantibody-drug conjugate (ADC). Examples of such a “protein-drugconjugate” include the modes of use, such as “Protein 1-drug” and“Protein 1-linker-drug.” As a drug, an anti-allergic agent or the likecan be used. Such a conjugate can be produced by a method well known toa person skilled in the present technical field.

With regard to the pharmaceutical composition of the present invention,various dosage forms are used depending on usage. Examples of an oralagent include a tablet, a powder agent, a granule, a fine granule, and acapsule. Examples of a parenteral agent include an injection, inhalationpowders, an inhalation liquid, eye drops, a liquid agent, a lotionagent, a spray agent, nasal drops, a drip, an ointment, a suppository,and a patch.

The pharmaceutical composition of the present invention is administeredby various administration methods, depending on usage. Examples of theadministration method include oral administration, intravenousadministration, intraperitoneal administration, subcutaneousadministration, topical administration, and intramuscularadministration.

The pharmaceutical composition of the present invention is preparedusing the protein of the present invention and at least onepharmaceutical product additive. The pharmaceutical composition of thepresent invention can be prepared by a known pharmaceutical method,depending on its dosage form. Examples of such a pharmaceutical productadditive include an excipient, a disintegrator, a binder, a lubricant, adiluent, a buffer, a tonicity agent, a preservative, a stabilizer, and asolubilizer. The above-described pharmaceutical product additive alsoincludes a physiological saline and water for injection. Thepharmaceutical composition of the present invention can be prepared bybeing mixed with, being diluted with, or being dissolved in theabove-described pharmaceutical product additives.

When the pharmaceutical composition of the present invention is used forprevention or treatment, the dose of the protein of the presentinvention, which is comprised therein as an active ingredient, isdetermined, as appropriate, depending on the age, sex, and body weightof a patient, the degree of disease, a dosage form, an administrationroute, etc. With regard to the dose applied to an adult by oraladministration, the applied dose can be determined, for example, in therange of 0.1 μg/kg to 1000 mg/kg/day. The daily dose in the case of oraladministration is preferably in the range of 0.1 mg/kg to 10 mg/kg/day,depending on the dosage form. Such a daily dose may be administered atonce, or dividedly over two or three administrations. Moreover, the doseapplied to an adult by parenteral administration can be determined inthe range of 0.01 μg/kg to 1000 mg/kg/day. The daily dose in the case ofparenteral administration is in the range of preferably 0.1 μg/kg to 10μg/kg/day, 1 μg/kg to 100 μg/kg/day, or 10 μg/kg to 1000 μg/kg/day,depending on the dosage form.

EXAMPLES

The content of the present invention will be described in more detail inthe following examples and test examples. However, these examples arenot intended to limit the scope of the present invention.

Example 1 Expression and Preparation of Protein 1 (1) Preparation ofProtein 1 Expression Vector

cDNA encoding the amino acid sequence shown in SEQ ID NO: 3 wasincorporated into a mammalian expression plasmid vector to prepare aProtein 1 expression plasmid.

(2) Preparation of Protein 1-Expressing Cells

The Protein 1 expression plasmid was introduced into Chinese hamsterovary cells (CHO) to establish a Protein 1 stable expression cell line.Secretion of Protein 1 into a culture supernatant was confirmed bySDS-PAGE.

Test Example 1 IgE Binding Inhibitory Activity (IgE NeutralizingActivity) (1) Preparation of Assay Plate

Protein 1 was dissolved in a coating buffer, and an aliquot of theobtained solution was added onto a microplate. The microplate was leftat 4° C. for 18 or more hours, and was then washed with a washing buffer(PBS-Tween 20). Thereafter, a blocking solution (Assay Diluent) (BDBiosciences) was added thereto. The microplate was left at roomtemperature for 1 hour, and the blocking solution was then removed. Theplate was washed with a washing buffer, and was then used in themeasurement of binding inhibitory activity.

(2) Method of Measuring Binding Inhibitory Activity

Using omalizumab (anti-human IgE antibody) as a positive control, theIgE binding inhibitory activity of Protein 1 was measured by thefollowing method.

A certain amount of human IgE (ANTIBODYSHOP) was mixed with Protein 1 oromalizumab (Novartis) having any given concentration. The obtainedmixture was added to the plate prepared in the above (1), and it wasthen left at room temperature for approximately 2 hours. After the mixedsolution had been discarded, the plate was washed with a washing buffer.A HRP-labeled anti-human IgE antibody (BD Biosciences) was added to theresulting plate, and it was then left at room temperature forapproximately 1 hour. After the antibody solution had been discarded,the plate was washed with a washing buffer. A TMB(3,3′,5,5′-tetramethylbenzidine) solution was added to the plate. Aftera certain period of time had passed, phosphoric acid was added to theplate to terminate a coloring reaction. Thereafter, using a platereader, absorbance (OD450) was measured. Based on the amount of IgEbound to Protein 1 immobilized on the plate, Protein 1 and omalizumabwere evaluated in terms of IgE binding inhibitory activity (IgEneutralizing activity) (FIG. 1).

(3) Results

The Protein 1 of the present invention inhibited the binding of IgE toFCER1A in a concentration-dependent manner.

Test Example 2 Test Regarding Stability at Low pH (1) Preparation ofSample

A purification operation was carried out using AKTA Explorer 10 S (GEHealthcare). Protein 1 was allowed to be expressed by the same method asthat described in Example 1, and then, a culture supernatant thereof was2 times diluted with D-PBS(−) (Dulbecco's Phosphate Buffered Saline).The diluted solution was loaded on HiTrap rProtein A FF (GE Healthcare,17-5079-01). The above-described column was washed with D-PBS(−), andwas then eluted with a 100 mM glycine-HCI buffer (pH 2.2). A protein Aadsorption fraction was fractionated at 1.0 mL/tube. The peak fractionswere mixed with one another to obtain a low pH-treated sample (pH 2.9).The low pH-treated sample that had been preserved at 4° C. was used asan evaluation sample. 0.25 mL of an aliquot was sampled from theevaluation sample at a predetermined timing (5 to 12 days after thepreservation at 4° C.), and 0.05 mL of a 1 M Tris-HCI buffer (pH 9.0)was added to the aliquot to neutralize it, thereby obtaining aneutralized sample.

As a control, Fusion protein A described in Non Patent Literature 3 wasused. Fusion protein A was allowed to be expressed by the same method asthat described in Example 1, and then, a neutralized sample was obtainedby the same method as the aforementioned method. It is to be noted thatthe Fusion protein A used in the present test is a protein consisting ofthe amino acid sequence shown in the following SEQ ID NO: 4. The aminoacid sequence shown in SEQ ID NO: 4 comprises a linker fragmentconsisting of Asp at position 180 to Cys at position 188, and the numberof Cys residues contained in this linker fragment is 2.

SEQ ID NO : 4: VPQKPKVSLNPPWNRIFKGENVTLTCNGNNFFEVSSTKWFHNGSLSEETNSSLNIVNAKFEDSGEYKCQHQQVNESEPVYLEVFSDWLLLQASAEVVMEGQPLFLRCHGWRNWDVYKVIYYKDGEALKYWYENHNISITNATVEDSGTYYCTGKVWQLDYESEPLNITVIKAPREKYWLDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSL SLSPGK

(2) Method of Analyzing Content of Aggregates

With regard to the operation of analyzing aggregates, the content ofaggregates was confirmed by performing gel filtration chromatography ofusing Superdex 200 10/300GL (GE Healthcare, 17-5175-01), employing AKTAExplorer 10 S (GE Healthcare), and also using D-PBS(−) as a mobilephase. The areas of a peak whose eluted position was a monomer and anaggregate peak eluted in a high molecular region were calculated, and atransition of a change in the content rate of aggregates (%) in Protein1 and Fusion protein A, which was caused by a low pH treatment, wasevaluated (FIG. 2).

(3) Results

In the protein of the present invention, the increased level of theformation of aggregates associated with a low pH treatment time wassignificantly smaller than that in the case of Fusion protein A, andthus, the protein of the present invention exhibited high stabilityagainst exposure to low pH. Therefore, the protein of the presentinvention is excellent in terms of stability at low pH, and thus, theimprovement of purification efficiency and productivity is expected inthe production process.

Test Example 3 Test Regarding Stability Against Heat (1) Preparation ofSample

A purification operation was carried out using AKTA Explorer 10 S (GEHealthcare). Protein 1 was allowed to be expressed by the same method asthat described in Example 1, and a culture supernatant thereof was thenloaded on HiTrap Mab Select SuRe (GE Healthcare, 17-0034-94). Theabove-described column was washed with D-PBS(−) and a 100 mM citratebuffer (pH 4.0), and a protein A adsorbate was then eluted with a 100 mMglycine-HCI buffer (pH 3.3). A 1 M Tris-HCI buffer (pH 9.0) was added ata volume of 1/10 to the recovered fraction to neutralize it, so as toobtain a protein A-purified protein. The pH of this protein A-purifiedprotein was adjusted to pH 4.0 by addition of 1 N HCI, and it was thenloaded on a column filled with a mixed mode resin of hydrophobicinteraction and cation exchange. A non-adsorbed protein was washed witha 50 mM acetate buffer (pH 4.0), and 100% linear gradient elution wasthen carried out with a 50 mM Tris-Hcl buffer (pH 9.0). A peak fractionwas recovered to obtain a purified protein. The obtained protein wassubjected to gel filtration fractionation, using D-PBS(−) as a mobilephase, and employing HiLoad 16/60 Superdex 200 prep grade (GEHealthcare, 17-1069-01). A peak fraction corresponding to a monomer wasrecovered to obtain a gel filtration purified sample. This gelfiltration purified sample was adjusted again with D-PBS(−), and it wasthen poured into a microtube, followed by incubation at 37° C., so as toobtain an evaluation sample. An aliquot was sampled from this evaluationsample at a predetermined timing (1 day to 7 days after the preservationat 37° C.), so as to obtain a heat treatment sample.

As a control, Fusion protein A described in Non Patent Literature 3 wasused. Fusion protein A was allowed to be expressed by the same method asthat in Example 1, and then, a heat treatment sample was obtained by thesame method as the aforementioned method. It is to be noted that theFusion protein A used in the present test is a protein consisting of thesame amino acid sequence as that of the protein used in Test Example 2.

(2) Method of Analyzing Content of Aggregates

With regard to the operation of analyzing aggregates, the content ofaggregates was confirmed by performing gel filtration chromatography ofusing Superdex 200 10/300GL (GE Healthcare, 17-5175-01), employing AKTAExplorer 10 S (GE Healthcare), and also using D-PBS(−) as a mobilephase. The areas of a peak whose eluted position was a monomer and anaggregate peak eluted in a high molecular region were calculated, and atransition of a change in the content rate of aggregates (%) in Protein1 and Fusion protein A, which was caused by a heat treatment, wasevaluated (FIG. 3).

(3) Results

In the protein of the present invention, the increased level of thecontent of aggregates after preservation at 37° C. was smaller than thatin the case of Fusion protein A, and thus, the protein of the presentinvention exhibited more stability against exposure at 37° C. Therefore,the protein of the present invention is excellent in terms of stabilityagainst heat, as well as stability at low pH, and thus, the improvementof purification efficiency and productivity is expected in theproduction process.

INDUSTRIAL APPLICABILITY

Since the protein of the present invention has excellent neutralizingactivity against IgE, it can be used as a protein pharmaceutical productfor preventing or treating various diseases mediated by the IgE.

SEQUENCING FREE TEXT

-   SEQ ID NO: 2 Synthesized

All publications, patents and patent applications cited in the presentdescription are incorporated herein by reference in their entirety.

1. An Fc fusion protein comprising: (i) a high affinity IgE receptorα-chain; and (ii) an Fc region of IgG1, wherein a linker fragment regionbetween the (i) and the (ii) is the amino acid sequence shown in SEQ IDNO:
 2. 2. The Fc fusion protein according to claim 1, which is a dimer.3. The Fc fusion protein according to claim 2, wherein cysteine residuesin the linker fragment region form three disulfide bonds.
 4. Apharmaceutical composition comprising, as an active ingredient, the Fcfusion protein according to claims 1.